Mezoneuron hymenocarpum Wight & Arn. ex Prain

Prain, D. (1897) Journal of the Asiatic Society of Bengal. Part 2. Natural history 66(2): 233, 472. Type: Taong Doung, Burma, Herb. Wallich. 5832; iso: BM, K.

Usually grows as a vine but also flowers and fruits as a shrub. Vine stem diameters to 4 cm recorded. Spines often present on the stem. Spines recurved and very sharp. Pith rather large or hollowed out.

Leaflet blades sparsely hairy or +/- glabrous on the underside. Leaflet stalks about 1-2 mm long. Leaflets towards the base of the compound leaf are larger. Leaflet blades about 8-25 x 4-12 mm. Most spines recurved and present on the twigs and underside of the compound leaf rhachis but not on the underside of the secondary leaf axis.

Racemes about 20-40 cm long, combined into a panicle about 30-50 cm long. Pedicels about 8-15 mm long, pulvinate about 1-4 mm from the top. Petals: standard about 7-8 x 6 mm, claw about 7-8 x 6 mm, other petals about 7-10 x 10-11 mm, claw about 3-4 x 1.5-2 mm. Ovary glabrous, about 5 x 1 mm, ovules about 4-6, style about 12 mm long, funnel-shaped towards the apex.

Pods about 6-15 x 2-4 cm, not armed, winged (wing about 6-8 mm wide) along one margin. Seeds flat, ellipsoid, about 5-11 x 3-6 x 1 mm, about 1-6 per fruit. Testa pale brown. Cotyledons elliptic, about 9 x 7 mm, much longer than the radicle.

First pair of leaves bipinnate. Each bipinnate leaf consists of two branches (pinnae) and each branch has 6 glabrous leaflets attached. The lowest pair of leaflets are the smallest and the leaflets increase in size to the apical pair. Leaflet blades elliptic, oblong, oblanceolate or obovate, apices obtuse to retuse, bases oblique and rounded. Compound leaf petiole ending in an aristate process about 2 mm long. Petiole and compound leaf axes hairy. At the tenth leaf stage: leaf compound, bipinnate, each leaf with 3 pairs of branches (pinnae) bearing various numbers of leaflets so that the compound leaf consists of 50-60 leaflets. Compound leaf axis armed with spines at the attachment points of the secondary axes. Stems clothed in spines. Stipules about 1 mm long. Seed germination time 18 to 21 days.

Occurs in CYP and NEQ. Altitudinal range from near sea level to 250 m. Grows in gallery forest and vine thickets. Also occurs in Asia and Malesia.

Caesalpinia hymenocarpa (Prain) Hattink, Reinwardtia 9: 35 (1974).